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Gas Tungsten Arc Welding Handbook
A penetrant test is particularly useful on
nonmagnetic materials, where a magnetic particle test
cannot be used. Penetrant tests are used extensively
for exposing surface defects in welds on aluminum,
titanium, magnesium, and austenitic stainless steel
weldments. Figure 18-5 shows how penetrant inspec-
tion can also be used to detect leaks in both open-top
and sealed tanks or vessels. The penetrant is sprayed
around all the weld areas. Penetrant works by capil-
lary action and will identify any weld discontinui-
ties or defects. When testing a sealed tank, the dye
is sprayed (or brushed) on the external sides of the
welds. The two types of penetrant tests are dye pene-
trant and fl uorescent penetrant.
A dye penetrant test requires the surface of the
weld to be sprayed generously with penetrant and
allowed to soak for a specifi ed time. Excessive pene-
trant is then removed with an aerosol cleaner. All of
the penetrant is then wiped from the weld area. After
the penetrant is removed, the developer is applied. The
developer is a powdery white substance that is lightly
applied from an aerosol can. Any imperfections in the
weld will hold the dye and bleed through the white
developer, identifying the problem. A dye penetrant
test can be done anywhere because it is portable, and
it can be done in any position. The results can be
detected in normal light, without the use of special
equipment.
A B
C D
Figure 18-4. Dye penetrant test sequence. A—The penetrant is applied to the weldment. B—The penetrant is cleaned
off the weldment. C—The developer is applied to the weldment. D—The weldment is inspected for discontinuities that
appeared after the developer was applied. (Mark Prosser)